The present disclosure is related to digital electronic circuits, and more specifically to a pulse generator circuit optimized for printed, solution processed thin-film devices.
A pulse generator, also called a monostable multivibrator or one-shot, is a common element of many circuits in a wide range of applications. One common use is for switch debouncing. Another is as a reset signal generator. The input to a one-shot is an edge or pulse and the output is a positive or negative voltage pulse. The duration and magnitude of the pulse can be fixed or settable and are generally constrained to fall within ranges specified for the application. FIG. 1 shows a timing diagram of an example of a one-shot circuit.
A common circuit implementation of a monostable multivibrator includes an inverter and a NAND or NOR gate. FIG. 2 is an example of such an implementation. This circuit is a rising-edge-triggered negative pulse generator. In this circuit, input signal In is normally low, and inverter output D is high, making output signal Out high. When a rising edge is sent to In, output Out switches to low until the edge propagates through the inverter to D. Once D switches to low, Out returns to the high state. The duration of the pulse is determined by the propagation delay through the inverter. This can be controlled by the sizes of the transistors making up the inverter and NAND gate and/or by including additional delay elements, such as additional inverters or capacitors, to the D signal. Of course, many other implementations are known in the art.
There is a desire to produce devices such as the aforementioned monostable multivibrator using printed thin-film processes such as, but not limited to, those employing organic thin film (OTF) material systems. OTF fabrication processes are much less mature than crystalline silicon technologies, and direct implementation of conventional complementary designs is challenging due to the relatively low yield, high variability, and instability of devices formed by printed OTF processes. For example, in certain of such process reliable fabrication of all integrated devices in a single process is problematic. Further, according to some OTF processes, only one or the other of N- and P-channel devices may be formed (not both simultaneously). In processes capable of producing both N- and P-channel devices, one device type often has significantly higher performance than the other. And, process-based limits on device size in combination with large parasitic capacitances limit design of devices having desired pulse widths.
In light of these limitations, there is a need in the art for a device design capable of use within the context of OTF processes, such as circuit designs that include a minimum number of thin-film transistors (TFTs) and a single polarity. Such are disclosed herein.